1. Field of the Invention
The present invention relates to an improved process for making alkoxysilane cluster compounds. Furthermore, the present invention also relates to novel alkoxysilane cluster compounds prepared by this improved process and their use in functional fluid systems.
2. Description of the Prior Art
U.S. Pat. No. 3,965,136, which issued to the present inventor on June 22, 1976, disclosed the preparation of alkoxysilane cluster compounds of the formulae: EQU RSi[OSi(OR').sub.3 ].sub.3 (I)
or, written in an other form: EQU RSi[SiO.sub.4 ].sub.3 [R'].sub.9 (IA)
wherein R is hydrogen, an alkyl, alkenyl, aryl or aralkyl, and each R' is independently selected from the same group as R with the proviso that at least a majority of R' radicals are sterically hindered alkyl groups having at least 3 carbon atoms. These alkoxysilane cluster compounds of formulae (I) or (IA) have been disclosed to be very good functional fluids.
In particular, two different processes for preparing these alkoxysilane cluster compounds were disclosed in the forementioned patent. The first method of preparation involves the reaction of a trihalosilane with a trialkoxysilanol in the presence of a hydrogen halide acceptor base. The second disclosed method of preparation involves the reaction of a halosilane with an alkoxysilanol cluster compound in the presence of a base.
An optimization of the above-noted first method of preparation is disclosed in U.S. Pat. No. 4,077,993 which also issued to the present inventor on Mar. 7, 1978. This improved preparation method involves reacting a trihalosilane with a trialkoxysilanol in the presence of a critical amount of acceptor base in a solvent reaction medium while maintaining the reaction temperature in a select range.
It has been found that these methods for preparing alkoxysilane cluster compounds of the formulae (I) or (IA), above, are best suited to those particular compounds where R' is derived from either a secondary or tertiary alcohol. Specifically, it has been found that silanol intermediates HO--Si(OR').sub.3 are more stable when the R' radicals thereof are derived from secondary or tertiary alcohols (e.g., sec-butanol and tert-butanol). And, it has also been found that these more stable intermediates realize greater yields of the desired alkoxysilane cluster product.
In comparison, when the R' groups are sterically hindered alkyls derived from primary alcohols, such as 2-ethylhexanol or 2-ethylbutanol, the preparation of silanols HO--Si(OR').sub.3 is usually more difficult and the yields of these silanols are generally lower. Furthermore, the handling of these silanols with primary R' groups is also difficult because of poor storage stability.
In view of these preparation and handling problems, alkoxysilane cluster compounds with R' being a primary hindered group (i.e., as oppposed to a secondary or tertiary hindered group) have not been made in large commercial quantities. Furthermore, alkoxysilane cluster compounds with R' containing functionalities like fluoro groups, hydroxy groups, and cyano groups are also difficult to prepare and handle when the above-mentioned methods of preparation are employed. Accordingly, a new method for preparing such alkoxysilane cluster compounds where R' is either derived from a primary alcohol or contains functionalities like fluoro groups, or both, is needed. The present invention, as described in detail below, provides a solution to this need.
Still further, the specific alkoxysilane cluster compounds disclosed in the examples in the above-noted U.S. patents only contained one R' species for each compound. Mixtures of different R' in the same alkoxysilane cluster compound have never been specifically disclosed before the present invention.